The objective of this study is to understand the normal and abnormal physiology of the sensory cells and neuronal systems in the mammalian cochlea. The sensory inner and outer hair cells of the organ of Corti are responsible for receiving acoustic information and transducing the basilar membrane mechanical motions into a neural code. Knowledge of how cells functions is essential to other studies which attempt to assess and prevent hair cell loss; the most common denomination of deafness. Hair cell function, in this study, will be measured using intracellular recording techniques. The ac and dc receptor potentials, resting membrane potentials, and sounde-voked cell resistance changes will be recorded for both outer and inner hair cells. A variety of acouostic stimuli will be used to stimulate the cells including pure tones, pure tones in acoustic noise, and two-town combinations. The performance of the hair cells will be characterized for the changes induced by sound and electrical stimulation of the efferent nervous system to the cochlea. These efferent stimulation experiments should help reveal the true purpose of this neural component to organ of Corti. The endocochlear potential will also be manipulated through the administration of the diuretic Furosemide and with direct current, in order to determine if it is required for the high sensitivity and frequency selectivity of hair cells. The sound varying input resistance of inner hair cells also will be measured in order to determine if the extracellular potentials of the cochlea have a role in producing the low-frequency responses of auditory afferent nerve fibers. Recorded hair cells will be positively identified by iontophoretic injection of horseradish peroxidase and subsequent histochemistry and light microscopic inspection of the organ of Corti surface preparations.